Preparing cheese curd

ABSTRACT

A continuous process for preparing cheese curd from milk which includes the sequential steps of (a) deaerating the milk, (b) cooling the deaerated milk, (c) adding acid to the cooled milk in a manner which provides substantially instantaneous acidification of the milk but which avoids localized overacidification, (d) immediately heating the acidified milk by passing it through heat exchange means to coagulate the curd-forming elements in the milk and form curd, (e) periodically momentarily reversing the flow of the coagulating milk during passage through the heat exchange means, (f) cutting the formed curd as it emerges from the heat exchange means, (g) cooking the cut curd, (h) cooling the cooked curd, (i) draining the whey from the curd and (j) washing the curd.

United States Patent Wakeman 5] Feb. 29,1972

[54] PREPARING CHEESE CURD [72] Inventor: Alden H. Wakeman, Lake Mills,Wis.

[73] Assignee: Wisconsin Alumni Research Foundation,

[63] Continuation-in-part of Ser. No. 754,823, Aug. 23,

1968, abandoned.

OTHER PUBLICATIONS l-lanrahan, et al., New Type Pasteurizing,Deodorizing, and Concentrating Equipment for Use in Cheese Manufacture.J. Dairy Science Vol.42, 1959 (p. 907) SF 22118.

Primary Examiner-A. Louis Monacell Assistant Examiner-D. M. NaffAttorney-Howard W. Bremer [57] ABSTRACT A continuous process forpreparing cheese curd from milk which includes the sequential steps of(a) deaerating the milk, (b) cooling the deaerated milk, (c) adding acidto the cooled milk in a manner which provides substantiallyinstantaneous acidification of the milk but which avoids localizedoveracidification, (d) immediately heating the acidified milk by passingit through heat exchange means to coagulate the curd-forming elements inthe milk and form curd, (e) periodically momentarily reversing the flowof the coagulating milk during passage through the heat exchange means,(f) cutting the formed curd as it emerges from the heat exchange means,(g) cooking the cut curd, (h) cooling the cooked curd, (i)

1 draining the whey from the curd and (j) washing the curd.

6 Claims, 6 Drawing Figures PAIENIEBFEB 29 1972 SHEET 1 [IF 3 ATTORNEYPm'smmmzs m2 3, 645,751

SHEET 2 OF 3 INVENTOR ALDEN H. WAKEMAN ATTORNEY PAIENTEUFEB2919723,645,751

SHEET 3 OF 3 HEAT EXCHANGER TUBES TNT AIR CY LINDER I TIMER AIR CYLINDER"-TIMER INVENTOR.

ALDEN H. WAKEMAN ATTORNEY PREPARING CHEESE CURD This application is acontinuation-in-part of application Ser. No. 754,823, filed Aug. 23,1968 now abandoned.

This invention relates to an improved method for making cheese curd.More particularly, this invention relates to an improved method formaking cheese curd on a continuous basis. Still more particularly, thisinvention relates to an improved method for making cheese curd on acontinuous basis wherein a water-soluble food-processing grade acid isutilized to adjust the pH of the milk to within the isoelectric range ofthe casein present in the milk. 7

As a matter of convenience the following discussion will be directed tothe application of the method of this invention in the making of cottagecheese curd. It is to be understood, however, that the method also findsready application in the preparation of curd adaptable for use in themanufacture of other cheese products.

Cottage cheese is conventionally made from skim milk by the addition ofa starter culture which contains acid-producing organisms, e.g.,Streptococcus lactis or Streptococcus cremoris. The acid produced insitu in the milk by the organism drops the pH and causes coagulation ofthe milk into a smooth firm gel from which the cottage cheese curd ismade.

Various improvements upon this method of making cottage cheese have beensuggested. See, for example, Ernstrom U.S. Letters Pat. Nos. 3,089,776and 3,298,836 which are directed to processes including the use of afood grade acid, such as hydrochloric, to induce coagulation of curdforming elements in the milk. The process of U.S. Pat. No. 3,298,836 isof particular interest since the present invention comprises certainimprovements in the continuous process disclosed and claimed in thatpatent.

It has been found that although the process of U.S. Pat. No. 3,298,836is eminently suitable for the production of cottage cheese from milkhaving a high nonfat milk solids content, the use of low solids milk,e.g., skim milk containing about 9 percent nonfat milk solids, generatedcertain operational difficulties. Also, the curd produced by the processof that patent was not consistently uniform in size or texture or in itsability to adsorb the creaming mixtures conventionally applied to drycottage cheese curd.

The present invention provides a process for producing cheese curd frommilk without limitation on the solids content of the milk and withoutthe disadvantages attendant upon earlier processes. Most importantly,this'invention provides a process for producing cheese curd from milk ona continuous basis over an extended period of time.

This invention resides in a process for treating milk to produce curdwhich comprises a series of sequentially practiced steps including:deaerating the milk; cooling the deaerated milk; adding acid to thecooled milk so as to substantially acidify the milk to the desired pHwithout localized overacidification; immediately heating the acidifiedmilk by passage through heat exchange means to coagulate the curdformingelement in the milk and form curd; periodically momentarily reversingthe flow of the stream of coagulating and coagulated milk during passagethrough the tubes of the heat exchange means whereby a reverse shearaction between the coagulum and the walls of the heat exchange tubes iscreated and sticking of the coagulum to the said walls is therebyprevented; cutting the curd emerging from the tubes of the heat exchangemeans; cooking the cut curd; cooling the cooked curd; draining the wheyfrom the curd; and washing the curd.

1f the ends of this invention are to be realized, i.e., if continuouscurd production over an extended period of time is to be achieved withconcomitant consistency in curd size, texture, and creamingcharacteristics, careful attention must be given to four of the steps inthe above process. In all cases the practice of these four steps isessential to the achievement of the desired results. The four essentialsteps in the order in which they occur in the process as set forth are:

1. deaeration of the milk to be processed;

2. substantially instantaneous acidification of the milk with a foodgrade acid without localized overacidification;

3. a periodical momentary reversal of the flow of the coagulating milkduring passage through the tubes of the heat exchanger;

4. cooking the curd at a temperature in the range from about 170 to 184F. The other steps of the process as outlined can be carried out inaccordance with the practices and under the conditions conventional inthe art and particularly as set forth in U.S. Letters Pat. No.3,298,836.

It is to be understood that the cooking temperature range specified instep (4) above is essential to the making of cottage cheese curd havingthe desired characteristics. This cooking temperature range will bedifferent if the process of this invention is to be used for preparingcheese curd other than cottage cheese curd and in such circumstances maynot comprise an essential element in the process. Thus, and dependingupon the particular type of cheese curd being prepared, an appropriatecooking temperature can comport with known practices in the art or canreadily be determined by means of a preliminary trial. For example, inthe preparation of cheddar cheese curd the cooking temperature must becontrolled so that the desirable organisms present in the curd and whichare essential to the later curing process are not destroyed. lt is alsoto be appreciated-that the equilibrium pH of the acidified milk willvary depending upon the particular cheese curd being prepared.

in its entirety, and as practiced in the manufacture of cottage cheeseutilizing in part the apparatus of U.S. Letters Pat. No. 3,465,439,issued Sept. 9, 1969, in the name of A. H. Wakeman, D. C. Roahen and R.L. Knox, the process of this invention comprises:

1. substantially completely deaerating a stream of milk containing fromabout 8 to about 40 percent nonfat milk solids;

2. cooling the stream of milk to a temperature in the range from about35-50 F.

3. continuously adding to the stream of cooled milk and mixingintimately therewith, a water-soluble, food-processing grade acid, e.g.,hydrochloric acid, in an amount sufficient to acidify the milk to anequilibrium pH in the range from about 4.5 to about 4.7 when at atemperature of about 70 F., under conditions which substantially avoidany local overacidification and which provide substantiallyinstantaneous acidification of the milk stream;

4. substantially immediately following the acidification, heating thestream of acidified milk to a temperature in the range from about toabout F. by passing the stream in nonturbulent flow and in thesubstantial absence of interparticle motion through heat exchange meanswhereby the acidified milk is coagulated and the resulting curd is set;

5. periodically and momentarily reversing the flow of the coagulatingand coagulated stream of acidified milk during passage through the tubesof the heat exchange means whereby a reverse shear action between thecoagulum and the walls of the said tubes is created and sticking of thecoagulum to the said walls is prevented;

6. cutting the curd into substantially uniform segments as it emergesfrom the heat exchange means;

7. cooking the cutc8 curd by passage of the cut curd and whey throughheat exchange means wherein the temperature of the curd and whey israised to from about 170 to about 1 84 F.;

8. cooling the curd and whey to a temperature below about F.;

9. draining the whey from the curd; and

10. washing the curd.

FIGS. 1 and 2 taken together are representative of apparatus in whichthe process of this invention can be readily practiced.

FIGS. 3, 4, 5, and 6 are representative of apparatus which is suitableto periodically momentarily reverse the flow of the coagulating andcoagulated stream of milk in the heat exchanger in which the curd informed,

In the application of the present process for the manufacture of cottagecheese, for example, and referring to the drawings, 10 represents astorage tank for holding a supply of acidified milk for use in theprocess. Prior to placement in tank the milk must be deaerated, andacidified-essential steps in this process.

In traditional cottage cheese making procedures little difficulty isencountered in obtaining a suitable curd as a result of theincorporation of air in the curd since during the normal quiescent holdperiod in the vat before and while gelation is taking place air has timeto escape. In continuous processes, however, where curd formation takesplace in a very short period of time incorporation of air can adverselyaffect the curd texture and, as a consequence, acceptability of the curdin the market. Although in such continuous processes incorporation ofair sufficient to make the curd float is generally not encountered, ithas been found that air actually dissolved in the milk is at leastinpart retained in the curd as it forms and imparts to the curd amicroscopically spongy structure. Such structure is not considereddesirable since it affects the texture and feel of the curd when chewed.

To avoid such undesirable spongy structure the milk must be deaeratedand, after deaeration, processed through curd formation in a closedsystem to prevent to the greatest possible extent any reabsorptionormixing in of air.

Such deaeration can be accomplished by conventional means well-known inthe art and which employ heat treatment under vacuum. (See, for example,Modern Dairy Products by Lampert (1965) Chemical Publishing Co., NewYork, N.Y., page 176 for a typical piece of apparatus used for such apurpose.)

Following deaeration the milk is cooled, preferably to a temperature inthe range from about 35 to 50 F. and is then acidified with awater-soluble food-processing grade acid. The acid is added in an amountsufficient to produce an equilibrium pH in the milk of from about 4.5 toabout 4.7 when at a temperature of about 70 F. The acid must be addedand intimately mixed with the. milk in a manner which will providesubstantially instantaneous acidification of the milk, therebypreventing localized overacidification and precoagulation. Appropriatemixing can be accomplished by a number of means, but on a continuousflow basis it has been found that the desired rapid acidification can beobtained by impinging upon each other converging streams of milk anddilute acid. The violent mixing action obtained by this means effectssub stantially instantaneous acidification. It has been found that suchacidification improves curd tension when the curd is later formedresulting in a curd which resists fragmentation when mechanicallyhandled and since precoagulation is avoided, all of the coagulation tocurd is later accomplished in a quiescent state providing curdcharacterized by greater uniformity of size.

Following acidification it is preferable to begin heating of theacidified milk as soon as possible and thereby effect coagulation.Consequently, the amount of time the acidified milk is held in tank 10should be kept to a minimum and it may even be preferable to bypass tank10 and move the milk in a continuous stream from deaeration toacidification to coagulation.

Coagulation of the acidified milk is carried out in heat exchange means11, termed herein the curd former." Basically, the curd former comprisesvertically arranged tubes through which the acidified milk flows in anupward direction. The tubes are surrounded by a jacket within which aheating fluid is circulated and which heats the vertically disposedtubes. (A curd former of this type is more fully described in US.Letters Pat. No. 3,465,439 referred to above.) Tubes of relatively smalldiameter are used in the heat exchange means to permit the formation ofthe curd without turbulence, i.e., without interparticle motion, in theupwardly flowing acidified milk stream. As the acidified milk contactsthe heated tube wall it coagulates immediately adjacent the heated wall.Upon coagulation some whey is expelled between the coagulum and thewallto form a thin layer of liquid which then functions as a lubricantbetween the wall and the formed coagulum, allowing the formed coagulum(curd) to slip easily through the tube. As

the acidified milk progresses from the inlet end to the outlet end ofthe tube coagulation of the acidified milk progresses from the portionnearest the tube wall inwardly toward the center of the tube as heat isconducted toward the center of the moving stream. Thus, the coagulumcontrives to form a sleeve around the still liquid center portion of thecoagulating milk as it progresses through the heat exchange tube. Thespeed with which the acidified milk is forced through the tube and thetemperature of the heating medium in the surrounding jacket arecontrolled so that the milk is completely coagulated by the time itreaches the outlet end of the tube, from which the coagulum emerges inrodlike form and is cut to the desired length. It has been found thatheating of cool acidified milk product in the curd former to atemperature of about to l2 5 F. is adequate to induce formation of thedesired coagulum.

Certain difficulties have been encountered with such continuouscurd-forming procedure in that the formed coagulum does not always flowsmoothly through the heat exchanger tubes. At times, because oflocalized overheating perhaps, or for whatever reason, the coagulumsticks to the sides of the tube impeding flow through the tube and atworst completely plugging the tube. With the flow impeded by stickingcurd, the passage time through the tube increases, which means thecoagulum is exposed for a greater length of time to the heated tubewalls. This tends to create a type of case hardening on the rodlike curdand adversely affects the curd characteristics.

One of the features of the process of this invention prevents thesticking of the coagulum in the heat exchanger tube and thereby not onlyincreases curd consistency but makes possible extended continuousoperation on a practical and practicable basis since shutdownnecessitated by clogged tubes is virtually eliminated. This featurecomprises periodically and momentarily reversing the flow of the streamof coagulated and coagulating acidified milk in the heat exchanger tubesof the curd former. In general, this reversal of flow can beaccomplished by providing means whereby in a given interval of time theimput of acidified milk into the heat exchanger tubes from the tubeheader of the curd former is less than the output of curd from thetubes. Various means for achieving this end are depicted in FIGS. 3, 4,5 and 6 in which like numbered parts designate identical elements.

Referring to FIG. 3, ll designates in broken section the bottom portionof the curd former of FIG. 1. Also 15 designates the tube header of thecurd former and 16 the acidified milk inlet to the header. Furthermore17 is a schematic showing of a volumetric displacement device comprisinga chamber 18 and a piston 19 within the chamber. The piston 19 isconnected by a suitable rod to the piston in an air cylinder 20 whichfunctions to extend and retract the piston within the chamber 18 ina.timed sequence through connection with a timing device which controlsthe flow of air to one side or the other of the piston in air cylinder20 as is well known in the art.

In operation the volumetric displacement device of FIG. 3

functions as follows to periodically and momentarily reverse the flow ofcoagulating and coagulated acidified milk in the heat exchanger tubes.Milk, cooled and acidified, is pumped into header 15 at a constant rateby means of a positive displacement pump, filling the header and flowingup through the heat exchanger tubes where the coagulum is formed as setforth hereinbefore. From a fully extended position within the chamber 18the piston 19 is very rapidly retracted by operation of the air cylinder20. This rapid retraction of the said piston immediately increases thetotal combined volume of the header l5 and the chamber 18 so that suchcombined volume is greater than the volume of acidified milk flowinginto the header at that time interval. Since the curd former is shownmounted vertically this rapid increase in the combined volume of theheader and chamber causes the milk and coagulum in the tubes of the curdformer to momentarily reverse in flow, by the effect of gravity, in anattempt to fill the chamber and header. This sudden reversal of flowtends to create a reverse shear action between the tube wall and theformed coagulum within the heat exchanger tubes and prevents thecoagulum from sticking to the walls thereby eliminating thedisadvantages associated with such sticking, i.e., overheating of thecoagulum and the undesirable hard curd resulting from such overheatingand plugging of the tubes with coagulum. The piston 19 is then slowlyreturned to its fully extended position through operation of the aircylinder 20 so that only a rapid reversal of flow is obtained and noforward surge of milk and coagulum occurs in the tubes of the curdformer.

Although in the foregoing description and in the drawings the curdformer is shown in a vertical position and the volumetric deviceutilizes the force of gravity in performing its function, a horizontalarrangement of the curd former and/or of the volumetric displacementapparatus is equally operable. FIG. 4 is a schematic diagram of anapparatus which basically functions as does the apparatus of FIG. 3 toperiodically and momentarily reverse the flow of the milk and coagulumin v the curd former. In the apparatus shown, however, the air iscontinuously fed through line 21 to the underside of piston 19, which inthis embodiment is a floating piston and the rapid retraction of thepiston is realized by the opening of a large exhaust port, shown at 22,through action of the air cylinder 20 on a timed basis. Rapid exhaustionof the air under the floating piston through port 22 allows the statichead on piston 19 to quickly force the piston to the bottom of chamber18 thereby rapidly increasing the combined volume of the chamber andheader to greater than the volume of acidified milk flowing into theheader at that time interval and resulting in the effect described abovewith reference to FIG. 3.

Other methods of accomplishing the flow reversal are shown in FIGS. 5and 6. FIG. 5 shows a rubber tube 23 placed within a header theinflation and deflation of which changes the volume of the header. Thedotted lines indicate the position of the tube when deflated. Theinflation and deflation of the tube are accomplished through the timedaction of a threeway air valve 24, which allows a very rapid deflationto cause a sudden enlargement of the volume of the headerand a slowinflation so that only a rapid reversal of flow is obtained and noforward surge of milk and coagulum occurs in the tubes of the curdformer. I

In FIG. 6 the movement of the piston, rapid retraction and slowextension, is obtained through rotation of the dropoff cam 25 whichthrough linkage with motor 26, which has a variable speed drive, permitsflexibility in the timed sequence over which piston 19 is extended andretracted, the retraction and extension of the piston providing theperiodic and momentary reversal of flow as explained above in relationto the apparatus of FIGS. 3 and 4.

The position of the volumetric displacement device of the type shown inFIG. 3 with respect to the curd former is shown at 17 in FIG. 1.

The flow reversal in the curd former should be made to occur on aperiodic basis and hence in the illustrations of FIGS. 3, 4, 5 and 6 theflow reversal mechanism is indicated as being linked to a timingmechanism. The rate of repetition of flow reversal is not critical butin all cases should be such as will prevent the sticking of the coagulumto the tube walls. It is expected that this repetition rate may varydepending upon the type of cheese curd which is being made but such ratecan be readily adjusted through adjustment of the timing mechanismlinked to the flow reversal mechanism and the need for adjustment toprevent sticking can be readily determined from visual observation.

As the curd emerges in rodlike form from the tubes of the curd formeralong with whey it is cut into short lengths by a rotating knifearrangement at the top of the curd former, is cooled by mixing with wheywhich has been previously cooled, and is passed to surge tank 12 andfrom there to the cooker 13. The cooker is conveniently comprised ofthree stacked sections, each of which is susceptible of individual andseparate temperature control so that the curd and whey movessuccessively through three heating or cooling zones. A more completedescription of the cooker can be found in US. Letters Pat. No. 3,465,439referred to supra.

In the process of this invention, and utilizing the cooker (processor)of U5. Letters Pat. No. to 3,465,439, the curd and whey is maintained ata temperature of about to about 100 F. in the first zone of the cooker.This temperature is not critical but is maintained so that the curd andwhey is not suddenly exposed to the higher cooking temperatures in thesecond zone of the cooker.

An essential feature of the process of this invention is the cookingtemperature to which the curd and whey is exposed in the second zone ofthe cooker. In order to obtain the desired in characteristics it hasbeen found that this temperature must be maintained in the range fromabout [70 to about l84 F. and that the curds and whey must reach atemperature within this range. The residence time of the curds and wheyin the various sections of the processor will vary depending upon theflow rate through the processor. The essential factor in obtainingcheese curd having the desired characteristics is that the curds andwhey reach a temperature within the specified range and not the lengthof time they are maintained at such temperature. If the curds and wheydo not reach a temperature of about 170 a mushy curd which does not havethe desired firmness will result, while if a temperature in excess ofabout 184 F. is reached the formation of a highly undesirable gelatinousproduct tends to occur.

In the third zone of the cooker the curd and whey is cooled to at leastabout 145 F. and if desired, to the temperature of the first wash waterapplied i the conditioner l4, i.e., to about to F. Cooling to at leastabout 145 F. is essential to prevent the cooked curd from stickingtogether.

In normal operations in the preparation of cottage cheese curd the flowrate of the curds and whey through the cooker (processor) is regulatedso that the residence time in each of the three zones of the cooker isabout 6 to 7 minutes.

From the cooker the cooled curd and whey is delivered to the conditioner14 where the curd and whey are separated and the separated curd isrepeatedly washed with progressively cooler water, as is more fullydescribed in US. Letters Pat.

No. 3,465,439 supra, to avoid thermal shock to the curd. Also,

the final wash water may be acidified to adjust the acidity of the curd(see US. Pat. No. 3,298,836, column 5, lines l7-25).

As in the process of US. Pat. No. 3,298,836, the hydrochloric acidutilized for acidifying the milk in the aforedescribed process can bereplaced by other inorganic or mineral acids, such as phosphoric acid,or by organic acids such as acetic or lactic acid or by any equivalentwater-soluble acid which does not leave toxic residues when washed fromthe curd. Also, while the process eliminates the need for acid-formingbacteria, it will be understood that rennet in various amounts can beused, or flavor imparting agents commonly used in this art, e.g.,starter distillate, lactic acid, citric acid, can be employed ifdesired.

Having thus described this invention, what is claimed is:

I. A continuous process for preparing cheese curd which comprises:

a. substantially completely deaerating a stream of milk containing fromabout 8 to about 40 percent nonfat milk solids;

b. cooling said stream of milk to a temperature in the range from about35-50 F.;

c. substantially instantaneously acidifying the milk with awater-soluble, food-processing grade acid under conditions whichsubstantially avoid any local overacidification;

d. substantially immediately following said acidification, heating thesaid stream of acidified milk to a temperature in the range from about90 to about F. by passage of the said stream in nonturbulent flow and inthe substantial absence of inter-particle motion through heat exchangemeans whereby the acidified milk is coagulated and the resulting curd isset;

periodically and momentarily reversing the flow of said coagulating andcoagulated stream of acidified milk within said meat exchange meansduring said heating and curd formation whereby a reverse shear actionbetween the coagulum and the walls of the heat exchange means is createdand sticking of the coagulum to the said walls is thereby prevented;

f. cutting the set curd as it emerges from said heat exchange means;cooking the cut curd; cooling the cooked curd; and

i. washing the curd.

A continuous process for preparing cottage cheese curd which comprises:

substantially completely deaerating a stream of milk containing fromabout 8 to about 40 percent nonfat milk solids;

. cooling said stream of milk to a temperature in the rangev from about35-50 F.;

. continuously adding to said stream of cooled milk and in the rangefrom about to about F. by passage of the said stream in nonturbulentflow and in the substantial absence of interparticle motion through heatexchange means whereby the acidified milk is coagulated and theresulting curd is set;

e. periodically and momentarily reversing the flow of said coagulatingand coagulated stream of acidified milk within said heat exchange meansduring said heating and curd formation, whereby a reverse shear actionbetween the coa'guium and the walls of the heat exchange means iscreated 'and sticking of the coagulum to the said walls is therebyprevented;

f. cutting the set curd as it emerges from said heat exchange means;

g. cooking the cut curd by passage of the said out curd and whey throughheat exchange means wherein the tempera ture of the curds and whey israised to from about l70 to about 184 F.;

i. draining the whey from the curd, and

j. washing the curd.

3. The process of claim 2 wherein the food-processing grade acid isselected from the group consisting of hydrochloric acid, phosphoricacid, lactic acid and acetic acid.

4. The process of claim 3 wherein the food-processing grade acid ishydrochloric acid.

5. The process of claim 4 wherein the milk is whole milk. 6. The processof claim 4 wherein the milk is skim milk containing about 9 percentnonfat milk solids.

2. A continuous process for preparing cottage cheese curd whichcomprises: a. substantially completely deaerating a stream of milkcontaining from about 8 to about 40 percent nonfat milk solids; b.cooling said stream of milk to a temperature in the range from about35*-50* F.; c. continuously adding to said stream of cooled milk andmixing intimately therewith, a water-soluble, food-processing grade acidin an amount sufficient to acidify the milk to an equilibrium pH in therange from about 4.5 to about 4.7 when at a temperature of about 70* F.,under conditions which substantially avoid any local over-acidificationand which provide substantially instantaneous acidification of the saidmilk stream; d. substantially immediately following said acidification,heating the said stream of acidified milk to a temperature in the rangefrom about 90* to about 125* F. by passage of the said stream innonturbulent flow and in the substantial absence of interparticle motionthrough heat exchange means whereby the acidified milk is coagulated andthe resulting curd is set; e. periodically and momentarily reversing theflow of said coagulating and coagulated stream of acidified milk withinsaid heat exchange means during said heating and curd formation, wherebya reverse shear action between the coagulum and the walls of the heatexchange means is created and sticking of the coagulum to the said wallsis thereby prevented; f. cutting the set curd as it emerges from saidheat exchange means; g. cooking the cut curd by passage of the said cutcurd and whey through heat exchange means wherein the temperature of thecurds and whey is raised to from about 170* to about 184* F.; i.draining the whey from the curd, and j. washing the curd.
 3. The processof claim 2 wherein the food-processing grade acid is selected from thegroup consisting of hydrochloric acid, phosphoric acid, lactic acid andacetic acid.
 4. The process of claim 3 wherein the food-processing gradeacid is hydrochloric acid.
 5. The process of claim 4 wherein the milk iswhole milk.
 6. The process of claim 4 wherein the milk is skim milkcontaining about 9 percent nonfat milk solids.